Shear fragmenting bullet

ABSTRACT

A bullet has a jacket and a core seated into the jacket. The core consists of helically formed strands of malleable material swaged into a cylindrical shape. The strands have a uniform pitch along the core, and fragment uniformly into small portions upon impact. A method of making a bullet includes providing helically formed strands of malleable material, swaging the strands, and seating the strands into a jacket.

TECHNICAL FIELD

[0001] The present invention relates to firearm ammunition and moreparticularly to a jacketed bullet that shear fragments on impact and amethod of making the bullet.

BACKGROUND ART

[0002] It is desirable for a bullet to have good flight performance,including good range and accuracy, and limited penetration ability. Thedepth of bullet penetration is directly proportional to velocity andsize. Bullets that fragment prior to impact or immediately upon impacthave limited penetration ability. Such bullets have little or no path oftravel after impact, and therefore will not ricochet or pass through theintended target and strike an unintended target. However, bullets thatfragment or disintegrate before impact may not be able to achieve desireflight performance.

[0003] U.K. Patent No. 11,087 to Weiss discloses a hollow base bulletwith a mantle and a core pressed into the mantle through an openposterior end. The mantle is weakened by grooves in the anterior end.The core is a single solid leaden piece with incisions therein, orseveral twisted pieces of lead wire. Wiess states that the disclosedbullet will pass through a target and burst on impact with a hard body.

[0004] U.S. Pat. No. 122,620 to Maduell discloses an unjacketed bullethaving four interlocking segments. The segments of Maduell wouldseparate upon firing, and prior to impact, from a rifled firearm barreldue to centrifugal force.

[0005] U.S. Pat. No. 3,208,386 to Schneider et al. discloses a bullethaving several elongated metal segments with the ends of the segmentsfitted into a base cup, and the segments are then swaged to form thedesired bullet shape. The bullet of Schneider et al. separates uponfiring and prior to impact due to centrifugal force to provide a shotguntype pattern.

[0006] U.S. Pat. No. 5,569,874 to Nelson discloses a bullet having alarger central copper wire and several smaller copper wires around thecentral wire, with the tail ends of the wires swaged into a jacket.After impact the tip ends of the wires separate while the tail ends ofthe wire are retained in the jacket.

[0007] U.S. Pat. No. 5,528,989 to Briese discloses a bullet having ajacket and a leaden core with the core being formed by swaging aplurality of straight wires into a cylinder. The wires, after swaging,interlock with each wire having end sections that extend parallel to thelongitudinal axis of the core. Each wire has a kinked intermediatesection that includes two oblique sections, the oblique sectionsconnecting together and each oblique section connecting to an endsection.

[0008] U.S. Pat. No. 5,679,920 to Hallis et al. discloses a bullet witha copper jacket and a core of segments of zinc, iron, steel or copper.The core is created by forming a hollow roll or cylinder of twistedwires, and work hardening the wires by high impact swaging to make thewires brittle. The wires in the core after swaging are distorted andhave an interlocking pattern similar to the pattern disclosed in U.S.Pat. No. 5,528,989 to Briese, and are not arranged helically. Thedisclosed bullet fragments upon impact with a hard barrier such as asheet of metal.

[0009] U.S. Pat. No. 5,582,255 to Hallis et al. discloses a bullet witha copper jacket and a core having wires of zinc, iron, steel or copper.The core includes heart having a plurality of wires extending parallelto the longitudinal axis of the core and a plurality of wires twistedaround the heart. The core is high impact swaged to deform the wires andto make the wires brittle. The disclosed bullet fragments upon impactwith a hard barrier such as a sheet of metal.

DISCLOSURE OF THE INVENTION

[0010] A fully jacketed bullet is disclosed including a metal jacket anda core. The jacket has a base and a cylindrical body extending from thebase. The core includes a plurality of strands of malleable materialhaving a low shear modulus. The strands are helically formed or twistedtogether, and swaged into a uniform cylindrical shape. The core isseated into the jacket and the jacket is then point formed. The methoddisclosed includes providing a plurality of helically formed strands,swaging the strands to form a uniform cylindrical core, providing ajacket, seating the core in the jacket and point forming the jacket. Thestrands each have a uniform pitch around the core so that the shock wavethat is created by the impact of the bullet and that travelslongitudinally rearwardly along the bullet, uniformly and predictablyshear fragments and disintegrates the strands.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Details of this invention are described in connection with theaccompanying drawings that bear similar reference numerals in which:

[0012]FIG. 1 is a side view of a bullet embodying features of thepresent invention.

[0013]FIG. 2 is a perspective view of the core of the bullet of FIG. 1prior to swaging.

[0014]FIG. 3 is a perspective view of the jacket and core of the bulletof FIG. 1 after swaging of the core.

[0015]FIG. 4 is a top view of the bullet of FIG. 1 prior to pointforming.

[0016]FIG. 5 is sectional view taken through the line 5-5 of FIG. 4.

[0017]FIG. 6A is a side view of a core of a bullet with a plurality ofstrands parallel to the direction of travel.

[0018]FIG. 6B is a side view of the fragmentation pattern of the bulletof FIG. 6A upon impact.

[0019]FIG. 6C is an end view of the damage track of the bullet of FIG.6A.

[0020]FIG. 7A is a side view of a core of a bullet with two kinks in aplurality of strands.

[0021]FIG. 7B is a side view of the fragmentation pattern of the bulletof FIG. 7A upon impact.

[0022]FIG. 7C is an end view of the damage track of the bullet of FIG.7A.

[0023]FIG. 8A is a side view of a strand of a core of a bullet with asmoothly helically formed strands.

[0024]FIG. 8B is a perspective side view of the fragmentation pattern ofa core of a bullet having the strands of FIG. 8A upon impact.

[0025]FIG. 8C is a side view of the fragmentation pattern of the strandof FIG. 8A upon impact.

[0026]FIG. 8D is an end view of the damage track of the bullet of FIG.8A.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Referring now to FIGS. 1 to 5, a bullet 10 embodying features ofthe present invention includes a jacket 11 and a core 12. As shown inFIG. 2 the core consists of a plurality of strands 14, of a selectedlength, helically formed together in a spiral configuration so that eachstrand 14 extends rotationally around a longitudinal axis 15 of the core12 and obliquely to the axis 15.

[0028] The strands 14 are made of a malleable metal. Metals having a lowshear modulus are preferred. Lead, with a shear modulus of about 0.8million pounds per square inch (psi) or lead alloy are preferred. Othersuitable metals include tin and magnesium, both with a shear modulus ofabout 2.4 million psi, and aluminum, with a shear modulus of about 3.0million psi. Less suitable metals include copper and zinc, each with ashear modulus in the range of 6 million psi.

[0029] The helically formed strands 14 of the core 12 are low impactswaged into a uniform cylinder 16 as shown in FIG. 3. The term lowimpact swaging as used herein refers to swaging metal through highpressure, such as in a low speed hydraulic press, rather than through asudden, violent impact. Low impact swaging is distinguished from highimpact swaging in that high impact swaging uses a sudden, violent impactto form metal. High impact swaging work hardens metal and makes metalbrittle. The process of swaging bullets is known in the art, and welldescribed in U.S. Pat. No. 5,528,989, incorporated herein by reference.

[0030] Swaging the helically formed strands 14 of the core 12 provides adynamically balanced core 12 with no voids for good flight performance.Prior to swaging the helically formed strands 14 of the core 12 have amass slightly greater than the selected mass of the resultant cylinderso that excess material can be pushed out of bleed holes in the swagingdie and the core 12 for each bullet 10 for a specific application willhave exactly the selected mass.

[0031] The diameter of the combined helically formed strands 14 of thecore 12, prior to swaging, is slightly less than the diameter ofcylinder 16 and the length of the helically formed strands 14 of thecore 12 is slightly longer than the cylinder 16. Swaging compresses thehelically formed strands 14 of the core 12 so that the rotations perinch or pitch of the helically formed strands 14 of the core 12increases.

[0032] The jacket 11 has a base 18 and an elongated, hollow, cylindricalside wall 19 of uniform thickness, attached to and extending transversethe base 18. The length of wall 19 is greater than the length of core12. The base 18 and wall 19 form a cylindrical cavity 20 that is openopposite the base 18. The jacket shown has a flat base 18, however otherconfigurations are suitable, such as the rebated boattail. The diameterof the core 12 after swaging is slightly less than the diameter of thecavity 20 so that the core 12 may be readily inserted into cavity 20 andno air will be entrapped between core 12 and base 18 when core 12 isinserted into cavity 20.

[0033] As shown in FIGS. 4 and 5, the core 12 is seated in the jacket 11against the base 18 after insertion of core 12 into cavity 20. Theseating of core 12 includes pressing core 12 so that core 12 shortensand deforms outward to solidly contact wall 19. After the core 12 isseated in jacket 11, the bullet 10 is point formed such that the jacket11, opposite base 18, has an inwardly tapering tip 21, as shown inFIG. 1. The core 12 that extends into tip 21 will also be deformed intoan inwardly tapering configuration by the point forming.

[0034]FIG. 6A shows a bullet 30 with eight strands 32 that extendparallel to the direction of bullet travel. At impact the leading edgeof bullet 30 is momentarily compressed. This compression induces apressure wave that travels in the direction directly opposite the flightdirection of bullet 30. Bullet 30 may have a velocity of about 3000 feetper second. The pressure wave travels at the speed of sound. The speedof sound in lead is about 4000 feet per second. Therefore, the pressurewave travels rearwardly the length of bullet 30 before bullet 30penetrates the length of bullet 30.

[0035] The pressure wave separates the strands 32 as shown in FIG. 6B.The pattern of the damage track for the bullet 32 shown in FIG. 6Aresembles an eight pointed star as shown in FIG. 6C. The separation ofbullet 30 into the eight strands 32 significantly reduces thepenetration.

[0036]FIG. 7A shows a bullet 40, similar to several prior known bullets,with eight strands 42 that extend generally parallel to the direction ofbullet travel with each strand 42 having two kinks 43. The pressure wavecreated at impact travels parallel to, but in the opposite direction to,the direction of bullet travel. Strands 42, at the kinks 43, are notparallel to the direction of bullet travel. When the pressure wavereaches a kink 43, a shear stress is created in the strand 42. Strand 42breaks if the shear stress exceeds the shear fracture limit.

[0037] As shown in FIG. 7B, each strand 42 breaks at kinks 43 into threepieces, creating twenty-four fragments 44 from the eight strands 42. Thedamage track for the bullet 40 of FIG. 7A is shown in FIG. 7C and hastwenty-four spokes. Since each strand 42 separates into three fragments44, the penetration of bullet 40 of FIG. 7A is significantly less thanthe bullet 30 of FIG. 6A.

[0038]FIG. 8A shows a smoothly helically formed strand 14 of the bullet10 embodying features of the present invention. The strand 14 iscontinually oblique to the pressure wave, so the pressure wave producesshear stresses along the whole length of strand 14 and strand 14separates at shear fractures 24 into many fragments 23, as shown inFIGS. 8B and 8C. The fragments 23 are more nearly uniform in size thanprior known fragmenting bullets. FIG. 8C shows the damage track of thebullet 10. The damage track has a diffuse uniform circular pattern.Since each strand 14 of bullet 10 separates into many fragments 23, thepenetration of bullet 10 embodying features of the present invention issignificantly less than the bullet 40 of FIG. 7A.

[0039] The shear stresses increase as the angle of strand 14 increasesrelative to the direction of the pressure wave. The number of fragments23 increases, and the size of the fragments 23 decreases and thereforethe penetration depth decreases, as the pitch or turns per inch of thestrands 14 increases. The number of fragments 23 also increases as thenumber of strands 14 increases. Between one half and five turns aresuitable for the bullet 10, and between two and fifteen strands 14 aresuitable for bullet 10. Since the fragments 23 are more uniform in sizethan prior known bullets, the penetration and impact pattern of bullet10 are more predictable.

[0040] Bullet 10 has a full jacket 11 to minimize drag in flight and toassure that core 12 does not disintegrate prior to impact. Jacket 11 hasa uniform wall thickness for balance. Similarly, core 12 is swaged intoa uniform cylinder 16 for balance and further seated in jacket 11 forbalance. Bullet 10 must be well balanced to prevent tumbling anddisintegration before impact. Core 12 is preferably swaged into cylinder16 before seating so that each bullet 10 will have a uniform selectedprecise mass. Jacket 11 and core 12 do not have incisions or groovesthat would unbalance the bullet 10. Jacket 11 does not have grooves thatwould weaken the jacket 11 and cause the jacket 11 to burst from thepressure required to seat core 12.

[0041] The method of making the bullet 10 includes the steps ofproviding a plurality of strands helically formed together in a spiralconfiguration, low impact swaging the strands into a cylindrical corewith the strands maintaining the spiral configuration, providing acylindrical jacket with a closed base, seating the core into the jacket,and point forming the jacket opposite the base.

[0042] Although the present invention has been described with a certaindegree of particularity, it is understood that the present disclosurehas been made by way of example and that changes in details of structuremay be made without departing from the spirit thereof.

What is claimed is:
 1. A bullet comprising: a metal jacket, ofsubstantially uniform wall thickness, having an enclosed base and asubstantially cylindrical body extending transverse said base, and acore having a plurality strands of a malleable material having a lowshear modulus, said strands being helically formed together in a spiralconfiguration and swaged into a uniform solid cylinder having a selectedprecise mass, with each said strand extending rotationally and obliquelyin a continuous fashion around said cylinder, said core being seatedwithin said jacket against said base.
 2. The bullet as set forth inclaim 1 wherein said body of said jacket has an inwardly tapering tipopposite said base, said tip being created by point forming.
 3. Thebullet as set forth in claim 1 wherein said material of said strands hasa shear modulus less than 3.5 million pounds per square inch.
 4. Thebullet as set forth in claim 1 wherein said material of said strands ischosen from the group of lead, lead alloy, tin, magnesium and aluminum.5. The bullet as set forth in claim 1 wherein said plurality of strandsincludes from two to fifteen strands.
 6. The bullet as set forth inclaim 1 wherein each said strand has a pitch of between one half andfive turns per inch around said cylinder.
 7. A bullet comprising: ametal jacket, of substantially uniform wall thickness, having anenclosed base and a substantially cylindrical body extending transversesaid base, said jacket having an inwardly tapering tip opposite saidbase, said tip being created by point forming, and a core having fromtwo to fifteen strands of a malleable material, said material of saidstrands having a shear modulus of less than 3.5 million pounds persquare inch and being chosen from the group of lead, lead alloy, tin,magnesium and aluminum, said strands being helically formed together ina spiral configuration and swaged into a uniform solid cylinder having aselected precise mass, with each said strand extending rotationally andobliquely in a continuous fashion around said cylinder at a pitch ofbetween one half and five turns per inch, said core being seated withinsaid jacket against said base.
 8. A method of making a bullet comprisingthe steps of: providing a plurality of strands of helically formedtogether in a spiral configuration, said strands being of malleablematerial having a low shear modulus, swaging said strands into a uniformsolid cylindrical core having a selected precise mass, with each saidstrand extending rotationally and obliquely in a continuous fashionabout said core, providing a jacket, of substantially uniform wallthickness, having an enclosed base and a substantially cylindrical bodyextending transverse said base, and seating said core into said jacket.9. The method as set forth in claim 8 further comprising the step ofpoint forming said jacket after said step of seating said core, saidpoint forming creating an inwardly tapering tip on said body of saidjacket, opposite said base.
 10. The method as set forth in claim 8wherein said material of said strands has a shear modulus less than 3.5million pounds per square inch.
 11. The method as set forth in claim 8wherein said material of said strands is chosen from the group of lead,lead alloy, tin, magnesium and aluminum.
 12. The method as set forth inclaim 8 wherein said plurality of strands includes from two to fifteenstrands.
 13. The method as set forth in claim 8 wherein each said strandhas a pitch of between one half and five turns per inch around saidcore.
 14. A method of making a bullet comprising the steps of: providingfrom two to fifteen strands of helically formed together in a spiralconfiguration, said strands being of malleable material, said materialof said strands having a shear modulus of less than 3.5 million poundsper square inch and being chosen from the group of lead, lead alloy,tin, magnesium and aluminum, swaging said strands into a uniform solidcylindrical core having a selected precise mass, with each said strandextending rotationally and obliquely in a continuous fashion about saidcore at a pitch of between one half and five turns per inch, providing ajacket, of substantially uniform wall thickness, having an enclosed baseand a substantially cylindrical body extending transverse said baseseating said core into said jacket, and point forming said jacket aftersaid step of seating said core, said point forming creating an inwardlytapering tip on said body of said jacket, opposite said base